The present invention relates to variable delivery hydraulic pump control systems adapted for closed loop connection to reversible fluid motors, and it more particularly relates to pressure and flow control valve mechanisms adapted to be secured to the pumps for governing such systems.
A closed loop hydraulic system generally includes a variable delivery fluid pump which has a pump control valve mechanism in a housing secured thereto, the housing containing a directional control valve, and an override pressure responsive secondary valve for destroking the pump to override a flow designated by the extent of operation of the direction control valve in case of overload. Such a suystem is disclosed, for example, in the prior Weisenbach U.S. Pat. No. 3,166,891, granted Jan. 26, 1965 and assigned to the same assignee as the present invention. The above described mode of operation of the hydraulic system according to this patent is obtained by a feedback connection of a movable sleeve in each of the valves being positioned by feedback linkage connected to a flow control cam in the variable delivery pump. With such linkage connection, the direction control valve governs the direction and desired rate of flow of fluid in the closed loop, and the pressure responsive valve senses overload to destroke the pump as required to prevent stalling. To provide this mode of operation, a feedback cam is included in the feedback linkage, the feedback cam being designed to permit maximum pressure output of the pump at a minimum pump stroke position for utilization of full horsepower input to the system. An operator designates rate of flow but not precise pressure limits by the extent to which he operates his direction control valve lever from a normal center position.
An object of the present invention is to provide a variable delivery hydraulic pump control system which substantially obviates one or more of the limitations of the described prior art system.
Another object of the present invention is to permit an operator to designate maximum pressure for the system by the extent to which he actuates his direction control lever away from a normal position to which the lever is biased.
Another object of the present invention is to improve operating facilities of a closed loop hydraulic control system at minimum cost.
Other objects, purposes and characteristic features will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.